Electron-impact study of the S{sub 2} molecule using the R-matrix method
- Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India)
The present study deals with the calculation of elastic [integrated and differential cross section (DCS)], momentum-transfer, excitation, and ionization cross sections for electron impact on S{sub 2} molecules using the R-matrix method. The target states are represented by including correlations via a configuration-interaction technique. We used a double zeta plus polarization Gaussian basis set contracted as (12,8,1)/(6,4,1) for S atoms. The results of the static exchange, correlated one-state, and 20-state close-coupling approximations are presented. We have detected a stable anionic bound state {sup 2}{Pi}{sub g} of S{sub 2}{sup -} having the configuration 1{sigma}{sub g}{sup 2}{center_dot}{center_dot}{center_dot}5{sigma}{sub g}{sup 2} 1{sigma}{sub u}{sup 2}{center_dot}{center_dot}{center_dot}4{sigma}{sub u}{sup 2} 1{pi}{sub u}{sup 4} 1{pi}{sub g}{sup 4} 2{pi}{sub u}{sup 4} 2{pi}{sub g}{sup 3}. The vertical electron affinity value is 1.42 eV, which is comparable with the experimental value of 1.67{+-}0.015 eV. We detected two shape resonances, both of {sup 2}{Pi}{sub u} symmetry in the excitation cross sections of the {sup 1}{Delta}{sub g} and {sup 1}{Sigma}{sub g}{sup +} excited states. The dissociative nature of these resonances is explored by performing scattering calculations in which the S-S bond is stretched. These resonances support dissociative attachment, yielding S and S{sup -}. We have also predicted six resonances of various symmetries ({sup 2}A{sub u}, {sup 2}B{sub 1g},{sup 4}A{sub u}, {sup 4}B{sub 1g}) in the X {sup 3}{Sigma}{sub g}{sup -} {yields} B {sup 3}{Sigma}{sub u}{sup -} transition. We have calculated the DCS, in a correlated one-state model, by using the polydcs program of Sanna and Gianturco. The data from the momentum-transfer cross section, generated from DCS, are used to compute effective collision frequencies over a wide electron temperature range (200-30 000 K). The ionization cross sections are calculated in the binary-encounter Bethe model in which Hartree-Fock molecular orbitals at a self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals. We have included up to g-partial wave (l=4) in the scattering calculations. For this molecule we have used a Born-closure top-up procedure to account for the higher partial waves for the convergence of the cross section for the dipole-allowed excitation from the ground state. We have also evaluated the scattering length of the S{sub 2} molecule, which is equal to 2.615a{sub 0}.
- OSTI ID:
- 22095355
- Journal Information:
- Physical Review. A, Journal Name: Physical Review. A Journal Issue: 4 Vol. 84; ISSN 1050-2947; ISSN PLRAAN
- Country of Publication:
- United States
- Language:
- English
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